We present a quantitative analysis of the steady-state electronic transport in a resistive switching device. The device is composed of a thin film of Ag2S (solid electrolyte) contacted by a Pt nano-contact acting as ion-blocking electrode, and a large-area Ag reference electrode. When applying a bias voltage both ionic and electronic transport occurs, and depending on the polarity it causes an accumulation of ions around the nano-contact. At small applied voltages (pre-switching) we observed this as a strongly nonlinear current–voltage curve, which is modeled using the Hebb–Wagner treatment for polarization of a mixed conductor. This model correctly describes the transport of the electrons within the polarized solid electrolyte in the steady-state up until the resistance switching, covering the entire range of non-stoichiometries, and including the supersaturation range just before the deposition of elemental silver. In this way, it is a step towards a quantitative understanding of the processes that lead to resistance switching.